1. Field of the Invention
The present invention relates to an information signal discriminating apparatus adapted to ascertain the type of an information signal.
2. Description of the Related Art
The still video floppy system (hereinafter referred to as still video system) is a well-known conventional system for recording and reproducing FM-modulated image signals on and from a floppy disk having a diameter of 2 inches. In this still video system, the frequency allocation which is shown in FIG. 1 is adopted for the recording signal on such a floppy disk (hereinafter, the frequency allocation shown in FIG. 1 will be referred to as low-band FM signal frequency allocation). The luminance signal and the color-difference signals in the still video system are separately FM-modulated and recorded, as shown in FIG. 1. The R-Y signals and the B-Y signals among the color-difference signals are recorded alternately for each horizontal section. In the above low-band FM signal frequency allocation, the frequency of the FM luminance signal is 6 MHz at the sync. tip and 7.5 MHz at the white peak. As for the FM color-difference signals, the center frequency of the R-Y signal is 1.2 MHz, and that of the B-Y signal is 1.3 MHz. Further, index signals (hereinafter abbreviated as ID signals) having a carrier frequency of 204.5 KHz and adapted to represent such information as hours, minutes and seconds or day, month and year are frequency-multiplexed and recorded on the floppy disk. With the above-described low-band FM signal frequency allocation, a luminance signal band with a frequency of ca. 4.5 MHz and a horizontal resolution of ca. 350 in terms of TV lines is obtained. However, there is a demand for a wider luminance signal band since present-day TV monitors are equipped with higher resolution and wider screens than previous monitors. To meet this demand, recording and reproduction by such a frequency allocation as that shown in FIG. 2 has been conceived as the performance of recording media, heads, etc. has improved. In the frequency allocation shown in FIG. 2 (hereinafter referred to as high-band FM signal frequency allocation), the frequency of the FM luminance signal is 8 MHz at the sync. tip, and 10 MHz at the white peak. The FM color-difference signals and the ID signal have purposely not been changed in order to allow for interchangeability with the low-band FM signal frequency allocation. With this high-band FM signal frequency allocation, a luminance signal band with a frequency of 6.5 MHz and a horizontal resolution of ca. 520 in terms of TV lines is obtained. As the luminance signal band becomes wider in the manner as described above, it has become necessary for an apparatus equipped with a wider band to be also able to reproduce image signals recorded with the low-band FM signal frequency allocation so that interchangeability with a conventional apparatus may be retained. As a result, it has become necessary to conduct discrimination to determine which of the frequency allocations has been utilized in effecting the recording on the floppy disk. For this purpose, one idea that has been conceived contemplates information identifying which of the allocations has been employed being set in the above mentioned ID signal.
Since, however, the frequency of such an ID signal is rather low, the recording condition judgment can only be effected slowly with this system.